Year	Years
1970	1.96
1971	2.01
1972	2.06
1973	2.11
1974	2.17
1975	2.22
1976	2.28
1977	2.34
1978	2.4
1979	2.46
1980	2.52
1981	2.58
1982	2.65
1983	2.71
1984	2.78
1985	2.85
1986	2.92
1987	2.99
1988	3.07
1989	3.14
1990	3.21
1991	3.29
1992	3.37
1993	3.45
1994	3.53
1995	3.61
1996	3.69
1997	3.78
1998	3.86
1999	3.94
2000	4.03
2001	4.12
2002	4.21
2003	4.3
2004	4.39
2005	4.49
2006	4.58
2007	4.68
2008	4.78
2009	4.88
2010	4.98
2011	5.09
2012	5.19
2013	5.3
2014	5.41
2015	5.52